1. Field of the Invention
The present invention relates to a tracing control method and apparatus for causing a move point, which conducts the same movement as that of a locus tracer, to correctly trace an object locus. The method and apparatus can be applied to machine tools and robots, etc. The move point exhibits the same movement as a tool in a case where the method and apparatus is applied to machine tools, and that of a robot hand in a case where the method and apparatus is applied to robots.
2. Description of Related Art
FIGS. 9-11 illustrate a conventional tracing control method and a typical structure therefor, taking a model for tracing a locus C:y=f(x) drawn on a two-dimensional plane as an example for simplifying the explanation. In FIG. 9, a tracer a is moved in directions x and y by motors Mx and My, respectively, via ball screws, etc. In FIG. 10, position (x1, y1) is a present position of the tracer, and position (x1+.DELTA.x, y1+.DELTA.y) is a position where the tracer is required to be moved after the time period of .DELTA.t.
In the conventional control method, as shown in FIG. 11, at step 302, the positional element (y1+.DELTA.y) is calculated by the following equation: EQU y1+.DELTA.y=f(x1+.DELTA.x)
and a differential from the present position is calculated as (.DELTA.x, .DELTA.y).
Then, required drive speeds .DELTA.x/.DELTA.t and .DELTA.y/.DELTA.t in x and y directions, respectively, are calculated as step 303, and the calculation results are fed to drive motors Mx and My. Then, the drive motors Mx and My are synchronously driven at speeds .DELTA.x/.DELTA.t and .DELTA.y/.DELTA.t, respectively so that locus C is drawn by the tracer a.
However, the conventional control methods and apparatus have the following problems.
First, at a high speed and high load operation (for example, a state during machining in the case of a machine tool), the locus tracer deviates from an objective locus C, and the tracer cannot trace locus C.
Second, in the case of a two-dimensional and three-dimensional operation, two and three factors, respectively, need to be controlled, which is a accompanied by a cost increase.
The reasons for the generation of the above-described problems are as follows:
With respect to the first problem, in the conventional control method, locus C cannot be traced correctly if any one of the x-axis drive speed .DELTA.x/.DELTA.t and the y-axis drive speed .DELTA.y/.DELTA.t changes non-synchronously. At a high speed and high load operation, resistance acting on the tracer is large, which is likely to generate changes in the drive speeds.
With respect to the second problem, in the conventional control method, factors to be controlled in a two-dimensional operation are .DELTA.x/.DELTA.t and .DELTA.y/.DELTA.t and the number of the factors is two, and factors to be controlled in a three-dimensional operation are .DELTA.x/.DELTA.t, .DELTA.y/.DELTA.t and .DELTA.z/.DELTA.t and the number of the factors is three. Therefore, the same number of factors as that of dimensions need to be controlled.